OSI Model

Historically, one method of talking about the different layers of network communication is the OSI model. OSI stands for Open Systems Interconnect.

This model defines seven separate layers. The layers in this model are:

·         Application: The application layer is the layer that the users and user-applications most often interact with. Network communication is discussed in terms of availability of resources, partners to communicate with, and data synchronization.

·         Presentation: The presentation layer is responsible for mapping resources and creating context. It is used to translate lower level networking data into data that applications expect to see.

·         Session: The session layer is a connection handler. It creates, maintains, and destroys connections between nodes in a persistent way.

·         Transport: The transport layer is responsible for handing the layers above it a reliable connection. In this context, reliable refers to the ability to verify that a piece of data was received intact at the other end of the connection.

This layer can resend information that has been dropped or corrupted and can acknowledge the receipt of data to remote computers.

·         Network: The network layer is used to route data between different nodes on the network. It uses addresses to be able to tell which computer to send information to. This layer can also break apart larger messages into smaller chunks to be reassembled on the opposite end.

·         Data Link: This layer is implemented as a method of establishing and maintaining reliable links between different nodes or devices on a network using existing physical connections.